1. Field of the Invention
The present invention relates to a method of fabricating an electro-photographic photosensor such as a photosensitive drum of a copy machine.
2. Description of the Prior Art
An electro-photographic photosensor in which a photoconductive layer made of amorphous silicon (a-Si:H) is formed on a base made of aluminum has been widely used. The photosensor which uses as its base aluminum has the advantage of providing good electrostatic characteristics. However, such photosensor has the disadvantage that the long time employment may cause the amorphous silicon layer constituting the photoconductive layer to peel off because such amorphous silicon has inherently weakness in adherence to aluminum.
Therefore, in prior art, for example, in U.S. Pat. No. 4,416,962 "ELECTRO-PHOTOGRAPHIC MEMBER HAVING ALUMINUM OXIDE LAYER" Shirai et al., amorphous silicon used as the photoconductive layer is formed by an evaporated process on a surface of an alumite layer in which very small porosities formed in an oxidizing process have been processed to seal. As a result of that, the adhesive strength of the amorphous silicon to the aluminum base is enhanced.
FIGS. 1(a) and 1(b) show the surface of the aluminum base processed to the alumite and further to seal its porosities. More particularly, in the alumite process, by the process of electrolyzation using as an positive electrode an aluminum base 10 and as electrolyte sulfuric acid or oxalic acid, an alumite layer having a double structure of a porous portion (porous layer) 21 dissolved by the electrolyte and a remaining insoluble fine portion (barrier layer) 21 is formed as an oxide film of the positive electrode, as shown in FIG. 1(a). Further, after the above mentioned process, by processing said alumite layer to seal its porosities with high pressured vapor or boiled water, the porous layer of the alumite layer is chemically compounded with water, with the whole volume being swollen, and subsequently becomes a stable oxide film 23 sealed its porosities, as shown in FIG. 1 (b).
In the alumite layer formed by the alumite process, a thickness of the porous layer 21 made of amorphous Al.sub.2 O.sub.3 is in proportion to a duration of electrolyzation, while a thickness of the barrier layer 22 made of crystalline Al.sub.2 O.sub.3 is in proportion to electrolyzation voltage.
Usually, the diameter of each of the porosities in the porous layer 21 is about 100 .ANG. to 300 .ANG., and the density of the those porosities is about hundreds million to a thousand and several hundreds million per 1 mm.sup.2. Both of the diameter and the density are dependent on the condition of the electrolyzation.
In the case of an amorphous silicon photosensor which uses as its base aluminum, the adhesive strength of the amorphous silicon film to the aluminum base can be enhanced by forming a photoconductive film made of an amorphous silicon on the alumite film which has been previously formed on the aluminum base by the above mentioned process of sealing porosities. Such process enhances the adhesive strength to a certain extent, but cannot completely prevent the amorphous silicon film from peeling off.
Further, although the alumite process to the surface of the aluminum base enhances the adhesive strength as above mentioned, electrostatic characteristics of the electro-photographic photosensor is degraded by the process.